[ReactNative] Add RCTAssertThread and restrict -[UIManager addUIBlock:] to _shadowQueue

Summary:
@public

Add `RCTAssertThread` to `RCTAssert.h` for convenience when checking the current/queue,
it accepts either a `NSString *`, `NSThread *` or `dispatch_queue_t` as the object to be checked

Also add a check to `-[RCTUIManager addUIBlock:]` - There was a discussion on github (https://github.com/facebook/react-native/issues/1365)
due to the weird behavior caused by calling it from a different thread/queue (it might be added after `batchDidComplete` has been called
and will just be dispatched on the next call from JS to objc)

Test Plan:
Change `-[RCTAnimationExperimentalManager methodQueue]` to return `dispatch_get_main_queue()` and run the 2048 example,
it should dispatch with a helpful message (screenshot on the comments)

React/Base/RCTLog.h

@@ -42,18 +42,12 @@ typedef void (^RCTLogFunction)(
   NSString *message
 );
 
-/**
- * Get a given thread's name (or the current queue, if in debug mode)
- */
-RCT_EXTERN NSString *RCTThreadName(NSThread *);
-
 /**
  * A method to generate a string from a collection of log data. To omit any
  * particular data from the log, just pass nil or zero for the argument.
  */
 RCT_EXTERN NSString *RCTFormatLog(
   NSDate *timestamp,
-  NSThread *thread,
   RCTLogLevel level,
   NSString *fileName,
   NSNumber *lineNumber,